1. Field of the Invention
The present invention relates to devices for determining the profile of a surface and more particularly devices for determining the profile of the surface of a road or of a tunnel.
2. Prior Art
A device for determining the profile of a surface, comprising a source of a beam forming, on that surface, a light spot, means for that spot to move on the surface and a detection system whose axis cuts the beam in the vicinity of the surface to define a reference level, is known. The detection system comprises a photomultiplier tube of the type called a "scanning" tube, that is, comprising means for the electronic scanning of its receiving surface and on the other hand, a lens for forming an image of the spot on that receiving surface. The device further comprises, means for determining, by a measuring of the scanning time, the distance of the image from the centre of the receiving surface, that distance being representative of the difference between the light spot and the reference level.
That device has the disadvantage of being fairly inaccurate. Indeed, it is not possible to effect a sufficient number of measurements on a given surface, mainly because the photomultiplier scanning tubes have low resolution and scanning frequency characteristics.
The aim of the present invention is to overcome that disadvantage.